Sum Root to Leaf Numbers

Description

Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.

An example is the root-to-leaf path 1->2->3 which represents the number 123.

Find the total sum of all root-to-leaf numbers.

Note: A leaf is a node with no children.

Example:

Input: [1,2,3]
    1
   / \
  2   3
Output: 25
Explanation:
The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.
Therefore, sum = 12 + 13 = 25.

Example 2:

Input: [4,9,0,5,1]
    4
   / \
  9   0
 / \
5   1
Output: 1026
Explanation:
The root-to-leaf path 4->9->5 represents the number 495.
The root-to-leaf path 4->9->1 represents the number 491.
The root-to-leaf path 4->0 represents the number 40.
Therefore, sum = 495 + 491 + 40 = 1026.

Solution(javascript)

const sumNumbers = (root) => {
  const isLeaf = node => node && !node.left && !node.right
  const value = (current, v) => current * 10 + v
  const aux = (node, current) => {
    if (!node) {
      return 0
    }
    if (isLeaf(node)) {
      return value(current, node.val)
    }
    return aux(node.left, value(current, node.val)) + aux(node.right, value(current, node.val))
  }
  return aux(root, 0)
}